Automated fiber placement machines are nowadays widely used to manufacture parts, components and structures from composite materials. These systems typically comprise a fiber placement head spatially positionable by large envelope multiaxis positioners. The fiber placement head is operable to lay up carbon fiber composites and/or tape onto a stationary mold, i.e. tool.
The materials used in automated fiber placement heads are typically composed of unidirectional carbon fibers pre-impregnated into a resin and are provided as tapes, or thin strips, commonly known as “tows.” The term “tows” is used herein to collectively refer to tows, tapes, or plys thereof.
Each head is usually capable to lay and compact a plurality of tows arranged side-by-side to form a “ply” or “course” over and onto a tool. The head usually has all means to lay-up the tows/tape automatically such as a compaction roller, means to individually cut or add each tow whenever required as well as means to heat up the tows/tape and/or the substrate zone to ensure sufficient tack for tow/tape adhesion.
The head is also automatically fed by an integrated tow magazine (creel) which supplies the tow/tape in an organized array and with a correct tension. This tow/tape magazine system and fiber placement head are mounted at the ram end of the multiaxis positioner which under instructions provided by suitable control means is capable of following a desired multiple-pass lay-up path onto a stationary mold which remains stationary and is anchored to the ground. Because most of the tools upon which the tows/tape are laid upon have a double curvature contour or other complex geometry, the multiaxis positioners have at least five axes in order to properly position and maintain the compaction roller normal to the surface and/or tangent to the forming skin on the tool.
In all said arrangements, the mold or tool is kept stationary and the multiaxis positioner is moving the head system in space. Moving the head instead of the mold itself is desirable due to the fact that large part molds are very large in size and weight.
The only known exception to said arrangement is when large parts present a rounded shape. In such a case the part is moving, in particular it is rotated around a single center-line by means of an additional rotary motion, usually horizontal (e.g. the mold is placed between headstocks) or vertical (e.g. the mold is placed onto a rotary table). Said additional rotary motion is usually moving in concert with the positioner during the lay-up cycle or it is more simply used as an indexed motion with the purpose to bring a different portion of the mold inside the working envelope of the positioner.
Whether the large part is stationary or eventually spinning around a single center-line, once the lay-up cycle is completed, the replacement of the mold (now carrying a composite skin) inside the AFPM (Automatic Fiber Placement Machine) work zone, remains a delicate, time consuming and critical operation. The problem is aggravated if a different part mold is loaded inside said work-zone because it may require different clamping means for the proper anchoring of the mold to the ground. Moreover, moving the fiber placement head and its associated creel is not always the most efficient means of manufacture when smaller parts are taken into account. Yet further, attempting to move a large fiber placement head and its associated creel relative to a smaller part has proven to be quite difficult when the smaller part has complex geometry.
Efforts to manufacture small parts by using a floor-mounted stationary fiber placing head cooperating with a multi-articulated robot moving the part versus said head to perform the automatic layup are known. As an example, U.S. Pat. No. 8,758,538, the entire teachings and disclosure of which is incorporated herein by reference, teaches how a small part can be robotically moved against a plurality of stationary heads in order to obtain a multi-layer lay-up, with the possibility to receive different tows for each layer if necessary.
Although the system provides a workable solution for small composite parts manufacturing, it has major limitations. It has been discovered in fact that a substantial number of additional features are necessary in order to make possible a true automatic and flexible composite manufacturing system.
Most composite parts require multiple processes ranging from tape-laying to different tow size/composition. Additionally, some parts require a “sandwich” structure requiring an inter-laminar layup of foam, honeycomb layers or sealants that find the robot completely inadequate or unprepared to automatically apply such layers/materials whereas an operator could instead easily and efficiently perform such tasks.
Further, inter-process inspection is often a mandatory requirement and a second layer cannot even start without certifying that first layer quality meets the quality requirements and this can slow the robot significantly. In other words, the robot remains idle as the part is removed, inspected, and then placed on the robot again if it passes inspection.
Yet further, inter-process repair is often indispensable in order to proceed to the next step. Should the inspection of first layer discover discrepancies, a manual repair before proceeding to the next step is unavoidable, the option to scrap the part being economically unbearable. Given that it is quite common for such discrepancies to arise, the robot will again remain idle while repairs are completed.
Yet further, the automatic fiber placement heads as well as the creel, when mounted in a fixed orientation, are difficult to inspect and repair given their fixed orientation in space.
In other words, small composite parts cannot be manufactured in an efficient and reliable way unless the system provides a solution to the above identified requirements. Accordingly, there is a need in the art for an AFPM and associated methods that can readily manufacture smaller composite parts in an efficient and cost effective manner.
The invention provides such an apparatus and method. These and other advantages of the invention, as well as additional inventive features, will be apparent from the description of the invention provided herein.